FIG. 8 is an explanatory view for explaining operation of a conventional paperboard feeding apparatus of lead edge type; FIG. 9 and FIG. 10 are explanatory views for explaining nonconformity of the conventional feeding apparatus. In general, a feeding section of a box making machine for corrugated board sheets is an unit in which corrugated board sheets 1 piled up on a feeding table 16 are delivered successively one sheet at a time from the lowest layer through delivery rolls 4.
In the figure, a backstop 3 is constructed so as to be able to move longitudinally (between 3 and 3') on the feeding table 16 and to be fixed at any position corresponding to a length in feeding direction of the corrugated board sheets 1. The corrugated board sheets 1, which are charged from a preprocess not shown, drop when they abut against a front guide 2, and are piled up successively between the backstop 3 and the front guide 2. Further, a plurality of delivery rolls 4 are provided under the lowest layer sheet 1a in a state of projecting slightly above the feeding table 16. Besides, the inside of a suction box 6 is connected with a vacuum pump or a suction blower 8 through a duct 7.
In above-described construction, the suction box 6 is brought into an almost sealed state by covering the upper surface of the suction box 6 with the lowest layer sheet 1a so as to form a negative pressure region inside by operating above-mentioned suction blower 8, thereby to function so as to increase a frictional force Fo between the lowest layer sheet 1a and the delivery rolls 4. On the other hand, a frictional force F caused by the weight (direct pressure) of sheets which are piled up above a sheet 1b at the second step is generated on the top surface of the lowest layer sheet 1a, and the lowest layer sheet 1a is delivered by the difference between frictional forces generated on the top surface and the under surface of the sheet (delivery force applied to the sheet f=Fo-F), and is delivered further to a downstream process (printing section) by means of rotation so as to be put between field rolls 5a and 5b provided downstream.
In a conventional feeding apparatus described above, a gap at a lower end of the front guide 2 is set so as to be a little wider than the thickness of the paperboard 1 by means of a gap adjusting means not shown. Since the height of the tip of the paperboard 1 from the top surface of the feeding table 16 varies depending on the degree of a deformed state of the paperboard 1 such as a warping state (upward warping, downward warping) and a curved state, it has been required to readjust the gap every time such deformation occurs. Further, in case the above-mentioned gap is inappropriate, e.g., when the gap is small with respect to the upward warping deformation quantity as shown in FIG. 4 for instance, the tip of the sheet 1a collides with the lower end portion of the front guide 2. Furthermore, in a deformed state as described above, the negative pressure in the suction box 6 is not increased by the fact that outside air inflows from the gap at the tip of the sheet 1a, The frictional force Fo between the lowest layer sheet 1a and the outer peripheral surfaces of the delivery rolls 4 becomes smaller, and the sheet delivery force f is decreased. There has been a problem that such a tendency becomes more conspicuous as the sheet dimension gets longer since it almost corresponds to the warping deformation quantity of the sheet.
Further, when the gap at the lower end portion of the front guide 2 is set wide against sheet deformation (upward warping) in view of above-mentioned nonconformity, a phenomenon of feeding two sheets is generated in such a manner that the sheet 1b at the second step which is to be delivered in the next place is delivered simultaneously with the lowest layer sheet 1a to be delivered when non-deformed sheets are piled up as shown in FIG. 5.
As described above, in a conventional feeding apparatus, these unstable factors remain and drift in feeding timing (unevenness of drift quantity) occur easily, and have caused the deterioration of quality such as variation of printing positions in a following process. Furthermore, there has been a problem that, when a sheet delivery trouble such as a feeding mistake (two sheets feeding for instance) is generated, the machine has to be stopped to cope with the trouble, thus decreasing productivity remarkably.
Thus, a conventional feeding apparatus has not been provided with a function that deformed (warped upwardly or warped downwardly) paperboard can be delivered surely by having the paperboards engage with a delivery means. As a result, in such a method those deformed sheets are piled up on a table after correcting the warping deformation manually to some extent, or a feeding speed is reduced has been adopted. In such a method, however, correction not only takes time, but also complete correction is impossible. In a paperboard having a long dimension in particular, unevenness of warping deformation quantity is large, and variety of defective sheets of paper board are produced easily by a feeding mistake (such as two sheets feeding, no delivery and unevenness of feed timing). Further, the machine had to be stopped sometimes for repair of the worst trouble, and serious unstable factors such as deterioration of quality and productivity remained.
FIG. 11 and FIG. 12 are explanatory views for explaining construction and function (operation timing) of conventional feeding apparatus which have been proposed in specifications of U.S. Pat. No. 4614335, No. 4681311 and No. 4828244. As shown in FIG. 11, a feeding apparatus of this type is constructed in such a manner that corrugated board sheets 103 piled up on a feeding table 102 are made to pass through a gap formed at a lower end portion of a front guide 104 by the rotation of delivery rolls 105 so as to deliver one sheet at a time downstream successively from the lowest layer sheet 103a. Further, a suction box 106 connected with a suction blower 108 through a duct 107 is provided at a position under a part of the corrugated board sheets 103. The suction box 106 is brought into an almost sealed state by covering an upper adsorbing surface with above-mentioned lowest layer sheet 103a, and a negative pressure region is formed inside by the action of the suction blower 108, thereby to function so as to increase a frictional force Fo between the lowest layer sheet 103aand the delivery rolls 105 which are delivery means.
Further, in a delivery roll 105 section, a receiver board 110 which is disposed at a gap portion of the disposed delivery rolls 105 and in which a relative height from an outer peripheral surface of the rolls 105 is variable is provided. This receiver board 110 has the lowest layer sheet 103a which comes in contact with the delivery rolls 105 by vertical ascent and descent attached and released, and functions to descend the sheet 103a below a sheet pass-line so that the outer peripheral surfaces of the delivery rolls 105 and the under surface of the sheet come in contact with each other thereby to apply a rotating delivery force and ascends the sheet 103a conversely thereby to cut off the delivery function of the delivery rolls 105.
Now, above-mentioned corrugated board sheet 103 is delivered between downstream feed rolls 109a and 109b by means of the operation of a delivery force f=Fo-F generated onto the sheet at a frictional force Fo between the lowest layer sheet 103a and the delivery rolls 105 and a frictional force F between the lowest layer sheet 103a and the sheet 103b at the second step, and is delivered further to a following printing process by the rotation so as to be put between the feed rolls 109a and 109b.
FIG. 12 shows the operation of the delivery roll 105 and the receiver board 110 along the axis of ordinate against a machine feeding period (axis of abscissa). The corrugated board sheet 103a comes in contact with the delivery roll 105 by the descent of the receiver board 110, and is transferred by the accelerated rotation (peripheral speed) of the delivery roll 105. When transfer of the corrugated board sheets 103 is taken over at a point O.sub.1 where the accelerated rotation coincides with the peripheral speed of the downstream feed rolls 109a and 109b, the transfer function is released by the ascent of the receiver board 110 at almost the same timing. Besides, the delivery roll 105 continues to rotate and stops at a point O.sub.2 after making one rotation. In the delivery of the next sheet 103b after one cycle is completed, the delivery roll 105 is rotated again after descending the receiver board 110, thereby to deliver the sheet 103b downstream as described previously. By repeating the same operation successively thereafter, it is set so that piled up corrugated board sheets 103 are delivered successively from the lowest layer sheet.
A conventional feeding apparatus described above is constructed and functions as described above, however, there has been such a problem as follows. That is, it is constructed so that an ascent timing of the receiver board 110 which keeps contact with the delivery rolls 105 for sheet delivery is always fixed (no correcting function) against a descent timing. Therefore, when the dimension of the corrugated board sheet 103 gets longer, the increased frictional force (sliding resistance) F between the lowest layer sheet 103a and the sheet 103b at the second step is entirely borne by rotation with supporting between downstream feed rolls 109a and 109b, which produces a main cause for delay of feed timing. Further, there has been such a problem that the relative timing of the start timing (rotation start timing) of the delivery rolls 105 cannot be altered, but feeding slippage (unevenness of slippage quantity) varies whenever load conditions such as machine speed, weight of piled up sheets (length, number of piled up sheets) and sheet material (coefficient of friction) are varied, thus causing troubles in post-processes in addition to printing.
Accordingly, it has been required to provide a mark positioning means (unit) in each unit in order to correct slippage of feed timing in a following process. Further, above-mentioned problem has not only increased defective paper generating quantity, but also caused to lower productivity remarkably coupled with frequent order changes.
In a conventional paperboard feeding apparatus constructed as described above, the ascent timing of the receiver board which separates contact between a sheet and delivery rolls which are delivery means of the sheet cannot be altered, but a rear lower surface of the lowest layer sheet slides while in contact with the receiver board when the sheet dimension gets longer. Thus, the delivery resistance is increased, and delay in feed timing has been caused. Further, feeding slippage quantity (drastic unevenness of feed timing) varies every time load conditions such as machine speed, sheet weight (height and length of piled up sheets) and sheet material are varied, thus it has been required to perform mark setting for all the printing colors each time in a following process such as a printing section.
When another conventional feeding apparatus is described with reference to FIG. 13 to FIG. 15, FIG. 13 to FIG. 15 are explanatory views for explaining a construction of a conventional feeding apparatus of lead edge type and nonconformity in the apparatus, and FIG. 12 is an explanatory diagram for explaining an operation timing of the lead edge feeder. The structure of a conventional feeding apparatus will be described briefly hereafter. As shown in FIG. 13, a feeding apparatus of the present type is constructed so that corrugated board sheets 203 piled up on a feeding table 224 are delivered downstream one sheet at a time successively from a lowest layer sheet 203a through a gap formed at an lower end portion of a front guide 201 by the rotation of delivery rolls 204 provided under a sheet pass-line. A duct 225 is arranged under the corrugated board sheets 203 of this apparatus, and a suction box 206 connected with a suction blower 226 through the duct 225 is provided at a location under a part of the corrugated board sheets 203. The suction box 206 is brought into an almost sealed state by covering an upper adsorbing surface with above-mentioned lowest layer sheet 203a, thus forming a negative pressure region inside by the operation of a suction blower 226, and functions so as to increase a frictional force Fo between the lowest layer sheet 203a and delivery rolls 204 which are delivery means.
A receiver board 205 in which a relative height position with respect to the outer peripheral surfaces of rolls 204 is variable is provided at a delivery roll 204 section through holes formed at locations corresponding to the rolls 204. This receiver board 205 is constructed so that it may be ascended and descended, and detaches the under surface of the lowest layer sheet 203a which comes in contact with the delivery rolls 204 by ascent and descent of the receiver board 205. The receiver board 205 applies a rotational delivery force of the delivery rolls 204 by having the receiver board 205 descend from the sheet pass-line with respect to the sheet 203a, and has the receiver versely so as to cut off delivery function of the sheet 203a by the delivery rolls 204. Now, with above-mentioned structure, the corrugated board sheet 203 is subject to an interaction of a frictional force f=Fo-F generated on the sheet by the difference between a frictional force Fo generated between the lowest layer sheet 203a and the delivery rolls 204 and a frictional force F generated between the lowest layer sheet 203a and the sheet 203b at the second step. The sheet 203a is delivered by this force inbetween downstream feed rolls 207a and 207b, and delivered further to a following printing process P by rotation while being supported by the feed rolls 207a and 207b.
Next, an operation (function) of above-mentioned conventional feeding apparatus will be described. FIG. 12 shows the operation of the delivery rolls 204 and the receiver board 205 taken along an axis of ordinate against paperboard feeding period (axis of abscissa). As shown in the figure, the corrugated board sheet 203a comes in contact with the delivery rolls 204 by the descent of the receiver board 205 and is transferred by accelerated rotation (peripheral speed), and the transfer thereof is taken over at a point O.sub.1 where the rotation coincides with the peripheral speed Vo of the downstream feed rolls 207a and 207b. The delivery rolls 204 lose transfer function by the ascent of the receiver board 205 simultaneously with the taking over, and the delivery rolls 204 continue to rotate thereafter and stop at a point O.sub.2 after one rotation. When a next sheet 203b is delivered after completion of one cycle, the delivery rolls 204 are rotated again after descending the receiver board 205 so as to deliver the sheet 203b downstream. It is set so that piled up corrugated board sheets 203 are delivered successively from the lowest layer sheet side by repeating above-mentioned operation successively thereafter.
The illustrated conventional feeding apparatus is constructed and functions as described above, and has such problems as follows.
That is to say, because of a structure that the ascent timing of the receiver board 205 which interrupts the contact between the delivery rolls 204 and the sheet 203 for the purpose of sheet delivery is always constant (no correcting function) with respect to the descent timing, the increased frictional force (sliding resistance) F between the lowest layer sheet 203a and the sheet 203b at the second step has to be borne entirely by the rotation while being held by downstream feed rolls 207a and 207b as the dimension of the corrugated board sheet 203 gets longer, thus causing such a serious problem that the feed timing is delayed.
Further, as shown in FIG. 15, feeding slippage (unevenness of slippage quantity) is generated every time load conditions such as machine speed, weight of piled up sheets (length, number of piled up sheets) and sheet material (coefficient of friction) are varied, thus resulting in troubles frequently in a post-process such as printing. FIG. 14 shows variation of a distance x from a front end of a sheet to the printing start position O on above-mentioned load conditions. There is a tendency that the bigger the load becomes (A.sub.0 .fwdarw.A.sub.2) against reference setting load condition A.sub.0, the shorter above-mentioned x.sub.1 becomes, and, in contrast with this, the smaller the load reduces (A.sub.0 -A.sub.1), the longer the distance x.sub.2 becomes. Such a tendency is generated by the fact that frictional forces F and Fo on the top surface and the under surface of the lowest layer sheet 203a are varied by load variation, and the slippage quantity between the delivery rolls 204 and the lowest layer sheet 203a is varied. With this, relative positional relationship between the corrugated board sheet 203 and a printing plate 222 on a plate cylinder 221 in a printing section P varies, thus causing that a printing position slips fore and aft in the flow direction of the sheet 203. Besides, FIG. 15 shows above-mentioned tendency in the concrete, and shows a case x.sub.1 in which the feed timing is delayed with respect to a distance x.sub.0 to an ideal printing start position and a case x.sub.2 in which the feed timing is too early, respectively.
It has been heretofore required to provide a mark positioning means (unit) in each unit for the purpose of correcting slippage of the feed timing in a downstream printing process in order to eliminate such nonconformity. However, since feed slippage quantity as described above is not fixed, but is different for each sheet in many cases, only the correction in the printing process has not been satisfactory. Furthermore, above-described problems have caused not only to increase defective paper board generating quantity, but also to lower productivity remarkably coupled with frequent order changes.
As described with respect to above-mentioned related art, there has been such a serious problem in a paperboard feeding apparatus which has been available so far that unevenness of the sheet delivery timing caused by slippage quantity variation between a sheet and delivery rolls which are delivery means of the sheet is large, thereby to deteriorate the product quality (accuracy). In other words, feeding slippage (large unevenness in feed timing) is generated every time the load conditions such as machine speed, sheet weight (piled up height and length of the sheets) and sheet material are varied, and it has been required to perform mark positioning each time in a following process such as a printing section.